Interferons are in fact proteins synthesized by specific human cells in response to a viral infection. Depending upon the type of a cell-producer and specific structural and functional features of interferons they can be subdivided into three basic types, that is, alpha or leukocyte interferon produced by leukocytes, beta or fibroblast interferon produced by fibroblasts, and gamma or immune interferon produced by T-lymphocytes.
Apart from their antiviral activity interferons also feature antiproliferative activity and also effect the immune response. This enables one to regard drugs based on interferon as a potentially effective means for treatment of some malignant neoplasms. By now highly-purified preparations of human interferon have been produced, which are in effect a family of 13 to 15 closely related proteins, each being coded with its own structural gene in chromosome 9. However, isolation of leukocyte interferon from donor's blood fails to provide its production in an amount sufficient for extensive clinical application, since the interferon content of liter of blood is as a rule within 10.sup.5 AU, whereas a single effective dose of interferon intended for intravenous injection to a patient, amounts to at least 10.sup.6 AU proceeding from tentative clinical observations.
Known in the present state of the art are diverse methods for producing human leukocyte interferons, based on the use of a variety of strains of microorganisms as producer strains, into which individual genes of human interferon have been transferred by means of vector molecules. In particular, use is made of bacterial strains of Escherichia coli, Bacillus subtilis, Methylophilus methylotrophus, etc. as the producer strains (cf. European Patent EP No. 0062971A2, published in 1982, Int.Cl.sup.3. C 12N 15/00).
Microorganisms containing a plasmid with the inserted gene of human leukocyte interferon, produce interferon when cultivated under submerged aerobic conditions in nutrient media containing assimilable sources of carbon and nitrogen, mineral salts and growth factors.
Known in the art is a method for producing human leukocyte interferon alpha-2 (cf. British Pat. No. 2,079,291A, published in 1982, Cl. C 12N 15/00), wherein use is made of E. coli K-12, strain 294, obtained by inserting a recombinant plasmid pLeIFAtrp 2,5, wherein the gene of interferon alpha-2 is under control of the regulator regions of a tryptophane operon of E. coli.
The aforesaid strain is cultivated under submerged conditions in nutrient media, containing the sources of carbon and nitrogen, mineral salts and growth stimulants, in the presence of an antiobiotic.
The interferon yield, for the aforesaid producer, amounts to 2.5.times.10.sup.8 AU per liter of the culture liquid.
However, application of E. coli as an industrial producer suffers from some disadvantages. E. coli is assumed to be a conventionally pathogenic microorganism, although the various strains of this bacterium are permanently present in the intestinal microflora of human beings. This fact imposes especially stringent requirements upon purification of drugs produced on the base of E. coli and complete separation of the protein impurities and endotoxins, which in turn makes the interferon production process much more expensive and affects adversely the yield of pure end product. Moreover, all the heretofore-known laboratory strains of E. coli are susceptible to phagolysis, the number identified phages specific for E. coli amounting to several hundreds.
In addition, the method discussed above suffers also from a relative low productivity of the culture, whereby interferon isolation from the cellular biomass and its subsequent purification until a homogeneous state is obtained, is a labour-consuming procedure.